Snap acting thermally responsive element with contacts at the periphery thereof in rocking and sliding engagement with corresponding fixed contacts during snap action



Feb. 13, 1968 w. R. HARPER, JR 3,369,093

SNAP ACTING THERMALLY RESPONSIVE ELEMENT WITH CONTACTS AT THE PERIPHERYTHEREOF IN ROCKING AND SLIDING ENGAGEMENT WITH CORRESPONDING FIXEDCONTACTS DURING SNAP ACTION Filed Aug. 16, 1966 United States Patent3,369,093 SNAP ACTING THERMALLY RESPONSIVE ELE- MENT WITH CONTACTS ATTHE PERIPHERY THEREOF IN ROCKING AND SLIDING EN- GAGEMENT WITHCORRESPONDING FIXED CONTACTS DURING SNAP ACTION Walter Reeve Harper,Jr., Barriugton, R.I., assignor to Texas Instruments Incorporated,Dallas, Tex., a corporation of Delaware- Filed Aug. 16, 1966, Ser. No.572,702 3 Claims. (Cl. 200-122) ABSTRACT OF THE DISCLOSURE A bimetallicsnap-acting plate marginally carries on one side two oppositecurved-face contacts between which the plate centrally supports amovable insulated third contact. The curved faces of the marginalcontacts with sliding action rockingly engage one of two fixedconductive line terminals in a main circuit. From each line terminalextends a conductive finger. These fingers engage the other side of theplate, one opposite each of the two contacts at the plate margin so asto bias them into free rocking engagement with the two conductive lineterminals. When the plate snaps said two contacts move freely withoutrestricting movements of the plate margins and without breaking theelectrical connection in the main circuit. Thus the third contact ismoved by the plate with efiicient snap-action to and from an adjustablepart of a third line terminal which is in a control circuit. Theassembly of said two line terminals, fingers, plate and third contact iscarried in one housing. The third line terminal and its adjustable partare carried in a second housing. These housings are provided with arotary bayonet type coupling means for convenient assembly prior toscaling, so as coaxially to relate the movable third contact to theadjustable part of the third line terminal.

Among the several objects of this invention may be noted the provisionof an improved switch which will quickly snap open to break a relaycircuit in response to heating resulting from current flow in a motorcircuit or the like passing through the switch, without breaking themotor circuit, except through action of the relay circuit; and theprovision of a snap-acting switch of the type described which is lesscomplex, more reliable, lighter in weight and less expensive toconstruct and assemble than former relay switches of the same class.Other objects and features will be in part apparent and in part pointedout hereinafter.

The invention accordingly comprises the construction hereinafterdescribed, the scope of the invention being indicated in the followingclaims.

In the accompanying drawings, in which one of various possibleembodiments of the invention is illustrated,

FIG. 1 is a plan view of a switch made according to the invention;

FIG. 2 is a cross sectional view taken along line 22 of FIG. 1, partsbeing broken away;

FIG. 3 is a fragmentary cross section similar to FIG. 2 showing portionsof the switch in a moved position;

FIG. 4 is a fragmentary cross section view taken along line 44 of FIG.1; and

FIG. 5 is a fragmentary view looking along line 5-5 of FIG. 3.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings.

Referring to the drawings, the switch comprises a casing 1 molded from asuitable electrical insulating material, such as a phenolic resin.Casing 1 has holes 3 which are adapted to receive bolts or othermounting members (not shown) for attaching the casing to a suitablesupport, such as a compressor housing. Casing 1 has a well 5 whichincludes a lower generally cylindrical portion 7 and a somewhat largerupper cylindrical portion 9. The well is surrounded by a wall 11. Threesemicylindrical ribs 13 spaced 120 apart on wall 11 project radiallyinward into the upper cylindrical portion 9 of the well 5.

Well 5 receives the lower end portion of a head 15 which is made of asuitable electrical insulating material, such as a phenolic resin. Thecasing 1 and head 15 constitute the switch housing as a whole. Carriedin the head 15 is a conventional heater wire 16 connected with a heaterterminal 18. These parts 16 and 18 may be omitted, if desired. Head 15has a generally cylindrical outer wall 17 which is enlarged at its lowermargin to form a rim 19, the latter being substantially the samediameter as the cylindrical portion 9 of well 5. Rim 19 has threearcuate notches 21 spaced 120 apart. The notches extend the full heightof the rim and are adapted to receive ribs 13 on the casing as the baseis inserted into the well 5. The height of rim 19 is such that the upperend of the rim is just beneath the lower end of the ribs 13 when thebase is fully inserted into well 5 with the lower end of the baseengaging a shoulder 23 at the bottom of portion 9 of the well. Thispermits a bayonet type of connecting action, the head 15 being rotatedwithin the well 5 to unalign the ribs and grooves and to align one ofthe notches 21 with a hole 25 (FIGS. 2 and 3) in the casing so that alocking pin 27 can be inserted into the hole 25 and the notch 21 to lockthe casing and base in assembled relation. Then the space between thebase wall 17 and the well is filled with a sealing material 29. Thebayonet assembly arrangement facilitates assembly and reducesmanufacturing cost.

A downwardly opening generally cylindrical chamber 31 in head 15 ispartially closed by an annular baflle 33 seated against a shoulder inthe lower end of wall 17. Slots 35 and 37 extend through head 15 fromthe top of the head to the chamber 31. These slots receive switchterminals 39 and 41. The inner ends of the terminals are bent over toform contacts designated 43 and 45. The other ends of the terminalsproject above the head 15 and may be attached to suitable terminal leadwires (not shown) of a primary circuit, such as the start windingcircuit of a motor driving a refrigeration compressor. The circuitbetween contacts 43 and 45 is completed through a thermally responsivebimetal snapacting electrically conductive dished element 47 carryingcontacts 49 and 51 mounted on marginal portions thereof, the latterengaging contacts 43 and 45, respectively. The element 47 is preferablya dished bimetallic disc having one layer of a low thermal coefficientof expansion and the other layer of a somewhat higher thermalcoefficient of expansion so that upon heating and cooling of the memberit snaps between the positions shown in FIGS. 2 and 3. Element 47 isnormally heated as current is passed through it and in addition by theauxiliary heater, if used. The pairs of contacts 43, 49 and 45, 51 areheld in rocking engagement at all times by a pair of retainers 53, 55which pass through slots 35 and 37 and have fingers 57 and 59,respectively, at their lower ends..These fingers bear against the lowerside of the disc 47 at about the centers of the contacts to hold thedisc margin against vertical movement and thereby hold the contacts inrocking engagement. The other end portion of the retainers are curvedinto loops and bear against the top of head 15 to anchor the retainersin the slots 35 and 37.

A follower generally designated 61 is articulated with the center ofdisc 47 by a screw 63. The screw extends through a hole in the center ofthe disc and is threaded into a central dome-shaped portion of follower61. The

underside of the screw head is inwardly beveled. This and the dome shapepermit free movements ofarticulation. The follower 61 moves up and downwith vertical movements of the center portion of the strip 47, as isapparent from a comparison of FIGS. 2 and 3.

The follower is made from an electrical insulating material. In thebottom of follower 61 there is a slot 67 (FIGS. 2, 3 and 5) defined by apair of arcuate walls 69. A switch contact 71 has an end portionpositioned in slot 67 which is cemented to the follower by an adhesive73.'Contact 71 has an arm 75 projecting from the slot and through baffle33 into the lower portion of well 5. A crimp connector 77 attached to abraided flexible (pigtail) electrical conductor 79 is welded to arm 75of the switch contact 71. Another crimp connector 81 (FIGS. 4 and 5) isattached to the other end of conductor 79 and welded to the inner end ofa terminal 83. Terminal 83 is generally Z-shaped as shown in FIG. 4 andpasses through a slot 85 in casing 1. An end of terminal 83 projectsfrom the casing as shown in FIGS. 1 and 4 so that an electricalconductor (not shown) for a motor circuit can be attached to theprojecting end portion of the terminal.

A switch contact 89 is secured to an end of a screw 91, the latter beingadjustable toward and away from contact 71 through a threaded hole 93-in casing 1. Walls 69 straddle contact 89 and guide contact 71 intoengagement with contact 89 when the strip moves to its FIG. 2 closedposition. A terminal 95 surrounds the other end portion of screw 91.Terminal 95 and screw 91 are held in place by a lock nut 97 on thescrew. Terminal 95 constitutes another terminal for the secondary orpilot circuit controlled by operation of the switch.

By way of illustration, operation of the switch of the invention will bedescribed in connection with protection of the start winding circuit ofa motor driving a refrigeration compressor. This circuit is connectedacross terminals 39 and 41, or 39 and 18 if a heater is used, so that apermanent path for electric current is provided through contacts 43, 49,element 47, and contacts 51 and 45, to complete the circuit to thecompressor winding. This circuit path through the switch remains closedat all times due to the provision of retainers 53 and 55 which hold thecontacts 43, 49 and 45, 51 in rocking engagement. The start windingcircuit normally includes a contactor (not shown) controlled by therelay circuit connected across terminals 83 and 95. The path through theswitch for current in the relay circuit is from contact 83 through theflexible pigtail conductor 79 to contact 71, then through contact 89 andscrew 91 to terminal 95. Screw 91 is 'adjusted so that contacts 71 and89 are in engagement when the disc 47 is in the FIG. 2 position.

During normalstarting operation of the compressor, the current of itsdriving motor passes between terminals 39, 41 and along disc 47 whichheats the disc 47. When the disc becomes heated to a predeterminedcritical temperature it snaps from the FIG. 2 to the FIG. 3 position.This does not directly interrupt the current path through the switch tothe compressor start winding because the retainers 53 and 55 hold thecontacts 43, 49 and 45, 51 in rocking engagement at all times. However,this movement of the center portion of the disc 47 elevates the follower61 and the contact 71 secured to it. This separates contacts 71 and 89to open the relay circuit. The relay circuit, when opened, deenergizesthe contact-or in the motor circuit, thereby opening the motor circuit.After disc 47 has cooled to a predetermined low temperature, it snapsback from the FIG. 3 to the FIG. 2 position, thereby closing thesecondary or pilot circuit path through the switch so'that the contactorand the motor can be energized again. The temperature at which theswitch opens the contacts 71 and 89 in the pilot circuit is variable byadjusting screw 91 to vary the pressure exerted on the center of disc47. This provides desirable adjustment of the temperature (and thus thecurrent) at which the switch contacts 71, 89 are opened.

The switch is substantially smaller and less expensive than other relaycontrol devices for compressor motors. This reduction in size and priceresults from the novel arrangement of the parts of the switch and fromtheir joint operation. The rocking contacts maintained between contactsof the pairs 43, 49 and 45, 51 exert a wiping action which keeps themclean and of low contact resistance.

While snap-acting member 47 is shown as a dished disc, it may be ofother appropriately dished forms for obtaining snap action.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above constructions withoutdeparting-from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

What is claimed is:

1. A thermally responsive snap-acting switch comprising two spaced mainline terminals, a conductive thermostatic plate having a snap-actingdeformable portion, two contacts on one face of the plate disposed onopposite sides of said deformable portion, each contact shaped forsliding and rocking contact with one of said terminals, a conductivefinger extending from each of said terminals into conductive engagementwiththe opposite face of the plate adjacent one of said contacts to biassaid contact against the adjacent line terminal when the contact isstationary and when it slides and rocks whereby the contacts slide androck during snap action without separation from the line terminals, amovable third contact supported by said deformable portion of the plate,a third control line terminal having a conductive part positionedrelative to said third contact for engagement and disengagement therebywhen said deformable portion of the plate snap-acts in'response totemperature change.

2. A switch made according to claim' 1, wherein said two line terminals,fingers, plate and third contact are carried as an assembly in a firsthousing, said third line terminal and its adjustable conductive part arecarried as another assembly in a second housing, said housings beingprovided with rotary bayonet type coupling means holding them togetherwith said third contact and the conductive part of the third lineterminal being coaxially related.

3. A switch made according to claim 2, wherein said plate is in the formof a bimetallic disk the central portion of which is deformable, saidtwo contacts are located at opposite margins thereof and said thirdcontact is centrally located on said central deformable portion, saidfixed part of the third terminal being adjustable for calibration.

References Cited UNITED STATES PATENTS 2,127,575 8/1938 Thompson et al.200122 2,694,121 11/1954 Van der Pyl 200138 3,244,848 4/1966 Chapin etal 200-67 3,297,845 1/1967 Mertler 200-138 BERNARD A. GILHEANY, PrimaryExaminer.

H. A. LEWITTER, Assistant Examiner.

